Based on insufficient information, the following will do what you ask. You will need to list the names used in the string strNames each separated by |. The code should only add the colons where they are not present (based on your message text).
http://www.gmayor.com/installing_macro.htm
Code:
Sub AddColons()
Dim VName As Variant
Dim oRng As Range
Dim oRng2 As Range
Dim i As Long
Const strNames As String = "JOHN|JACK"
VName = Split(strNames, "|")
For i = 0 To UBound(VName)
Set oRng = ActiveDocument.Range
With oRng.Find
Do While .Execute(FindText:=VName(i), MatchWildcards:=True)
If oRng.Start = oRng.Paragraphs(1).Range.Start Then
Set oRng2 = oRng.Duplicate
oRng2.End = oRng2.End + 2
If Not oRng2.Characters.Last = ":" Then
oRng.InsertAfter " :"
End If
oRng.Collapse 0
End If
Loop
End With
Next i
End Sub